EEVblog #61 - Crystal Oscillator Drift

[MGARestoration]

Fastinating!

[thenaimis]

I know this is an old video, but Dave, didn't you basically implement a time interval counter? We used to use TICs but ultimately switched to HP5071 cesium clocks for our project, and the TICs fell out of use. TICs are definitely test equipment you can buy "off the shelf" :-)

[rainbowsalads]

why not have a master clock on the surface send out a ping to all the individual

modules through the water periodically, so when the data is gathered at the end of the experiment the pings along with the data can be realigned through time stretching? then the clocks can drift all they like. : )

[williefleete]

if a clock drifts by 20 seconds a day i'd eat my hat, i'd expect that from a mechanical escapement (a real good one at that)...

i've made picaxe based clocks using analogue clock tickers before which maybe lose maybe a few seconds a day. and a binary watch which i think gains less than a second a day using a 32.768 Xtal from a fax, and i usually set it to internet time regularly

[fridgebulb]

What about having a single "synch pulse" of a different frequency that they can all pickup, that would appear as a spike in the results they give, allowing all the other results to be lined up. Same idea as a clapboard they use when making films.

[Films4You]

Whats wrong with

Start data pulse.. Main Data... End data pulse

Then line up the Start/End pulses.

[gavins1910]

Great video, thanks!

[sostenuto]

Hi Dave, do you know if jitter in PLL's and xtal oscillators can be measured without expensive instruments, like with a scope, and how?

[yeoldeengineer]

@sostenuto If you want to measure jitter or phase noise, your measuring equipment always has to be better than the DUT by quite a margin. The triggering on a scope may do for relatively jittery square wave sources like a CMOS VCO, but hardly for an XO. Phase noise analyzers go to great lengths in cancelling the contributions of major phase noise sources.

I suggest you check out the websites of Leif SM5BSZ and Enrico Rubiola, those might give you an idea. Also look at drift cancellation.

[AxelTiger]

I like this guy but sometimes it hard to know if hes being sarcastic or not :P

[cj691]

Very interesting stuff! You make me further wish I could afford my EE degree without putting myself in massive amount of dept...

[Blix43]

That oscillator drift graph looked like a vagina.

[Films4You]

So how does my quartz crystal wristwatch stay spot on time for years, even temperature changing, shock, etc?

[EEVblog]

@Films4You It shouldn't. It is does it's pure luck. Regular watch crystals are usually only accurate to maybe 10-15sec/month.

[SolutionByEvolution]

Why didn't you maintain an average of several counts to reduce the effects of jitter instead of using a binning technique? The averaging number crunching could have been done by the PIC and the results sent to the PC to reduce interface burdens.

[goldenrebel1st]

@SolutionByEvolution I was thinking exactly the same thing. If this was a generic set of time-series data, you could end up with a completely wrong result by binning. But I assume Dave knew enough about the characteristics of the drift that he knew he could get away with that technique.

[raysolomon]

very good video.

[hitachi088]

Wow , Super Clear explanation ! 5 Star/+1

[LyndonSoulGroove]

Hi Dave just started a new Position In electronic calibration..new country too

enjoying these, do you have e-mail ..

[heroineworshipper]

We have to do that for sonar positioning, but just compare the total number of cycles on the crystal with the total number of cycles on the reference.

[joe72205]

at 13:55 some kind of background hum disappeared and it was much more pleasant!

[EEVblog]

That's mains hum through the battery charger. Normally I film on battery, but sometimes I forget and don't hear it until editing time.

[TheWelly888]

I wish I heard lectures like yours when I was at university 20 years ago! Only one grumble - the video freezes a lot even when the download is well ahead of the playback.

[aynair]

This is the best episode so far. Very systematic, informative and providing real life experience.

Thumbs up!

[19916718514]

really appreciate your video!Thanks!!

[killerman4ever]

Nice, learned something new again .

[aljaz55]

Do you have maybe a graph when the linear slope has not been removed?

This "SineFit8dayData.gif" does not give a real absolute difference from the stable source. I know the slope can be compensated in their software, but this shows only the "random" part of the drift, not the total error. Those totals can alco be interesting to look at :)

[EEVblog]

I may have one somewhere, I'd have to look.

In this application it's only this resultant "skew corrected" data we are interested in. As it's the maximum drift deviation over the recording period that is the concern. And it ain't as "random" as you might think, that's what makes it all very interesting. The one shown is about as "random" as you'll find, the majority are usually more sinusoidal in shape.

[mdmde]

Great video. IHow do you find the time to do

all this stuff?

[ihatespam1977]

Did you have to account for atmospheric pressure as well as temperature? Since the circuit was going underwater, the pressure inside the enclosure would also have stay with a certain tolerance.

[desertbard]

I remember in one radar system, the crystal oscillator OCXO in the tracker unit required 20 minutes to stabilize. As little as the grease from the technicians fingers could change the "oven's temperature" enough to send the chassis back for repair. We needed the trackers out ASAP. So failure rates were high once the trackers got into the field.